1. Field of the Invention
The present invention relates broadly to containers and is more particularly concerned with an apparatus and process for manufacturing a thermoplastic headpiece for a plastic or laminate tube having a fully molded sealing surface and a concentric orifice.
2. Prior Art
The manufacture of thermoplastic headpieces for plastic and laminate tubes is well known in the container art and is typified by U.S. Pat. No. 2,624,071 to Strahm, U.S. Pat. No. 3,260,410 to Brandt et al, and U.S. Pat. No. 3,207,833 to D'Errico.
Injection molding is conventionally used in the manufacturing process. This technique typically involves expulsion of molten thermoplastic material from an injection cylinder into a mold unit which has a cavity that includes a portion corresponding to the shape of the headpiece to be molded. The uppermost surface of the cavity, referred to as the sealing surface of the cavity, has an opening to permit conveyance of the thermoplastic material therethrough into the mold cavity. The mold unit also includes a housing or cover for covering the top of the cavity and a passageway extending through the cover which communicates with the opening in the sealing surface.
In order to form the headpiece, the injection unit engages the mold unit so as to permit conveyance of the thermoplastic material from the outlet of the injection cylinder, through the passageway in the cover and subsequently through the opening in the sealing surface into the mold cavity. The thermoplastic material is steadily injected until it fills the mold cavity. After solidification of the molten material, the headpiece is removed so as to permit finishing.
Traditionally, the injection and solidification processes produce extraneous thermoplastic material, referred to as flash, extending from the sealing surface of the headpiece that requires removal during finishing. This flash results from the material that solidifies within the passageway and remains attached to the sealing surface upon removal of the cover.
The solidified headpiece is subsequently positioned for finishing so that an automatic snipping or trimming device cuts the flash just above the sealing surface of the headpiece leaving thermoplastic projections extending from the sealing surface that often reach 0.030 inches in length due to manufacturing tolerances. Consequently, an undercut or snip well is required in the hollow of the cap so as to provide clearance between the underside of the cap and the projections. This undercut is standard in commercially available plastic caps for plastic tubes, however, in the pharmaceutical market and in other areas where metal caps and tubes are conventionally used, undercuts or snip wells are not built into the cap. Typically, the smooth finish provided on the sealing surface of the metal tube by a lathe type of tool eliminates the need for an undercut in the cap. A change from plastic caps to metal caps for flexible tubes would normally require a change in the metal cap mold to accommodate the thermoplastic projection that is both expensive and time consuming.
In addition, the traditional tooling presently used in the manufacturing process utilizes a mold unit which includes a male member positioned within a female member so as to produce the headpiece cavity and orifice. The male member, typically sways during the injection cycle and as a result the orifice is not concentrically positioned within the headpiece neck. Some commericially available metal caps are provided with an inner dome, in such cases a concentric orifice and smoothly finished sealing surface is necessary for this cap to properly seal on the headpiece.
There is a commercial need for a tube headpiece of plastic or laminate with a sealing surface capable of sealing flush against the underside of commercially available metal caps while being capable of providing a concentric orifice. In addition, it is desirable to have a headpiece that provides cost savings in the manufacture of a tube by eliminating the need for a snipping or trimming operation while providing a smoothly finished, fully molded sealing surface on a headpiece with a concentric orifice. Satisfying these needs would permit competitive pricing between plastic or laminate tubes having headpieces with smooth sealing surfaces and the metal tubes presently used in these markets.
It is therefore an object of the present invention to provide an apparatus and process for manufacturing a plastic headpiece that does not require an undercut or snip well in the hollow of the cap, and which, therefore, can seal flush against the underside of commercially produced metal caps.
It is an additional object to provide a molding apparatus and process for manufacturing a headpiece having a concentric orifice and smoothly finished, fully molded sealing surface without the need for shipping the extraneous material from the sealing surface of the headpiece in order to produce a finished product.
Other objects and advantages of the invention will be apparent as it is better understood from the following description, which taken in connection with the accompanying drawings, discloses a preferred embodiment thereof.